1. Technical Field
The present disclosure relates in general to optical and electronic devices, and more particularly, to fused films of all-inorganic colloidal semiconductor nanometer scale materials (“nanostructures”) including semiconductor nanoparticles and functional inorganic ligands, which may be employed in an optoelectronic device.
2. Background Information
Digital imaging of sensed electromagnetic wavelengths is widely used in medical, military, industrial, and scientific applications. Image sensors include arrays of pixelated semiconductors and/or active pixel arrays that are optically sensitive to light (or wavelengths of electromagnetic radiation) and convert the incident photons to electrons. These photodetectors are integrated in circuit, and with other electronic circuits to convert optical signals to electronic signals, to store charge accumulated by the pixels, to transfer the charge and/or signals from the array, to convert the analog into digital signals, and to process digital data to form still or video digital images.
Examples of image sensors include devices that use silicon for sensing, read-out electronics, and multiplexing functions. In some image sensors, optically sensitive silicon photodetectors and electronics are formed on the same single silicon wafer. In other examples, larger area, flat panel image sensors consist of a large array of pixels as part of an active matrix where each pixel has a thin-film transistor (TFT) that can be externally addressed. Existing TFT array architectures can be used for larger area image sensing, however, they cannot tolerate the high temperature deposition techniques for many photodetecting semiconductor materials.
Deposition techniques for certain compound semiconductor materials are not compatible with established silicon integrated circuits. In such systems a silicon electronic read-out array and wavelength radiation sensitive photodetector arrays are fabricated separately, resulting in a complex assembly procedure, low yield, poor resolution and higher manufacturing and assembling costs. In addition, traditional manufacture of semiconductor substrates and optically sensitive semiconductor layers are limited to rigid and relatively small area optoelectronic devices.
Prior methods for solution-based nanoparticle films include volume losses of 30% or higher which may leave voids, holes, cracks and other defects in the film that negatively affect optoelectronic performance and require post-treatment to repair. All-inorganic colloidal nanostructures including semiconducting nanoparticles can be processed in solution and/or included in inks that can be deposited on a suitable substrate. This solution-processing compatibility allows post-processing atop other integrated circuits. In addition, the fabrication of optically active films using all-inorganic colloidal nanostructure inks can be achieved at low temperature to accommodate additional device structures including existing and new TFT and organic substrate, and integrated circuit materials.
In conventional methods, long-chain, organic ligands that are linked to nanoparticles are exchanged for shorter organic or volatile organic or inorganic ligands that are vaporized during a subsequent heating (annealing, sintering) step to provide a film consisting mainly of nanoparticles and being substantially free of ligands. In other conventional methods, the nanoparticle ligands may be removed by soaking the deposited layers in a solvent that dissolves and thus dissociates the ligands from the nanoparticles. These methods may often result in poor fused film qualities that are not preferential for use in optoelectronic devices, because organic ligand materials may not be removed once the nanoparticle solutions are deposited and organic ligand materials act as insulating materials in the fused films.
It would be desirable to improve existing methods for producing optoelectronic devices with all-inorganic colloidal nanostructures.